A pseudo bass is used as a method of generating a bass lower than a band of a speaker or a headphone (hereinafter, collectively referred to as a speaker). When f1 is a frequency of the bass desired to reproduce, if a frequency f2 (double the frequency f1) and a frequency f3 (three times the frequency f1) are input to the speaker, a frequency difference (f3−f2) (in other words the original frequency f1) can be perceived by a user (listener).
For example, if signals of two frequencies whose greatest common divisor is 50 Hz (for example, a 100 Hz signal as a 2nd-order harmonic and a 150 Hz signal as a 3rd-order harmonic) are input to a speaker which is not able to reproduce a band of 50 Hz or less, the listener perceives the output as if a 50 Hz sound is being reproduced.
In the related art, for example, a reproduced sound under such conditions contains noise, which is still insufficient to generate a high-quality pseudo bass.